1. Field of the Invention
The present invention relates to booms and mast structures for supporting a load, and to those supporting torque-inducing loads. In particular, if relates to a boom structure that may be rotated, and a mast structure that may be elevated. More particularly, it relates to a boom and mast structure mounted on a mobile platform for deployment of a system for inspection of vehicles or containers.
A boom used to support a load at a distance from a vertical support must resist deformation resulting from the downward forces applied thereto by that load, and the torque created thereby. In addition, where that boom and load may be subject to acceleration resulting from translation or rotation, or other application of forces, in other than the vertical direction, the boom must also resist torsion along its long axis. The necessity of resisting torsion will be increased by a further load in the form of a vertical portion extending downwardly from its far end, which acts to intensify torsional effects created by movement out of the vertical.
A mobile transport may have a mast mounted thereon, and a boom mounted atop the mast, which is rotatable with respect to the mast, and which has a vertical portion supported by its far end. For use in inspection of vehicles or containers, the mobile transport may mount a transmitter and sensors, on the boom and the vertical portion, for inspecting vehicles or containers which pass below and inward of the boom as the mobile transport is propelled past those items. In this situation, in order to increase the accuracy of the inspection, it is particularly important to resist torsion and bending to minimize changes in the position of the boom relative to the transport. Further, where the mast is to be raised of lowered along a vertical axis, the system used to do so must also guide that movement, and resist torque created by the load of the boom and its load.
2. Background Art
A structure supporting a load at a distance is subject to both bending and torsional effects, particularly when a further perpendicular structure is supported at a distance from the point of support. The use of metal tubes or beams for constructing such structures is known, as is use of C-channel beams to resist torsion or bending. However, such structures, if relatively long, are subject to buckling if not reinforced, and may not be sufficient to resist higher bending and torsion loads. Construction, and reinforcement of, such a structure installed upon a mobile platform must also address weight concerns related to vehicle weight and stability. Further, such structures must also resist movement of the structure relative to the point of support. Previous devices disclosed in patents include the following:
U.S. Pat. No. 5,152,659 to Waka discloses a boom assembly having an inflection point therein that utilizes two opposing upper and lower welded C-channels to form a box structure. The booms are used to form the arms supporting the bucket of a bulldozer. Waka does not address the use of tubes, or other reinforcements.
U.S. Pat. No. 5,568,829 to Crawford et al. discloses a boom for a sliding boom delimber, for use in the logging industry, the boom utilizing a pre-stressed I-beam to enclose and support power and control cables to the delimbing apparatus attached at its end. Crawford et al. do not address the use of tubes, or other reinforcements.
U.S. Pat. No. 5,692,028 to Geus et al. discloses a x-ray examining apparatus mounted on a mobile vehicle, including a support structure and detectors mounted on the supporting structure. Geus et al. do not address construction of any boom, mast or other structure supporting the detectors, or how to minimize movement of the support structure relative to the vehicle.
U.S. Pat. Nos. 5,764,683 and 5,903,623 to Swift et al. disclose a mobile device for inspection of containers, including detectors that may be supported from a horizontal boom extending from the mobile device. Swift et al. do not address construction of a boom or mast supporting the detectors, or how to minimize movement of the boom relative to the mobile device.
In addition, a mast assembly is known for raising and lowering a load from a mobile platform; such structures often utilize a mast formed of a hydraulic piston. A lateral load, such as that resulting from torque applied by a boom in the present invention, may be applied. In the absence of a separate guiding system, lateral loading would be transmitted through the hydraulic seals (often O-rings) to the cylinder walls, which may unduly compress those seals, and cause failure of these seals. Because a hydraulic lift system can fail, permitting the mast to drop, such systems may include a latching mechanism, to support the mast and load in an elevated position. However, this adds weight and cost. Such structures do not address the torque and load concerns of the described inspection system.
It can be seen that the foregoing do not meet all of the needs for a boom and mast structure that is rigid and torsion-resistant, and resistant to buckling and undesirable movement.
The present invention provides a highly rigid, torsion-resistant, and buckle-resistant boom design, which may include a vertical portion, providing stable support for the supported load. This invention provides a horizontal boom section, and in a preferred embodiment includes a vertical boom section depending downwardly from the distal end of the horizontal boom section. In another preferred embodiment, the proximal end of the horizontal boom section is preferably mounted to a vertical support, such as an elevatable mast, permitting vertical movement of the boom/mast structure, and rotation of the boom structure.
In preferred mode of operation, a series of vehicles, typically tractor-trailer rigs, or cargo containers, are placed in a line parallel to the intended direction of travel of the mobile inspection unit which incorporates a preferred embodiment of the invention. The unit is propelled forward so that a scanning zone of an inspection system passes through each of the rigs or containers in succession. The data gained from these scans is viewed and interpreted by an operator in the mobile transport. Accurate alignment and minimized relative movement between the radiation source and the sensors is critical. Because the sensors are mounted upon the boom sections, it is important to increase the torsional and bending resistance, and the resistance to buckling, of those sections, particularly the horizontal boom section. Torsion forces may act upon the boom in a number of ways. For instance, forward acceleration of the mobile inspection unit, and the resistance to motion of the boom structure, will result in inertia opposing that acceleration. This effect will be increased where that resistance is placed at a distance from the source of support, such as the vertical boom structure, supported at the end of the horizontal boom structure. Other sources of torsional effects include wind resistance and accidental obstruction of the boom structure. Similarly, bending forces are present resulting from the weight of the sensors and the boom""s own weight.
In a preferred embodiment, a horizontal boom section includes a continuous inner tube, or rod, which runs the length of the horizontal boom section. This inner tube penetrates several flanges arrayed along the length of the boom section. The flanges are preferably perpendicular to the inner tube, and are joined to it at the penetration. Individual, discontinuous, outer tube segments are placed outwardly of the inner tube, preferably concentrically, between and abutting, but not penetrating, the flanges. The outer tube segments are joined at their ends to the flanges"" faces, preferably in grooves sized to those segments. Inward-facing C-channel beams, running the length of the horizontal boom section, are joined on their inward faces to the flanges"" side edges, preferably congruently. Tensioning cables provide upward support for the ends of the structure, and permit a torque to be applied to straighten the structure.
Preferably, the boom further includes a vertical boom section, including a set of continuous tubes, or rods, which run the height of the vertical boom section, and penetrate several flanges arrayed along its height. The several flanges are substantially perpendicular to the vertical, and preferably congruent to inward-facing C-channel sections. The C-channel sections run the height of the vertical boom section, and are joined to the flanges. In a particularly preferred embodiment, a joint is provided roughly in the middle of the vertical boom section, permitting the lower segment to be folded upwardly against the upper segment, reducing the overall length of the vertical boom section for ease of stowage.
In a preferred embodiment, in order to facilitate elevation and rotation of the boom relative to a mobile transport, a mast-head and mast assembly are provided. The horizontal boom section, to which the vertical boom section is preferably mounted, is mounted to a mast-head, which is itself mounted to a mast assembly. The mast assembly is mounted to the chassis of the mobile transport. A mast assembly includes a mast guide and an elevation system to elevate the mast and the boom structure supported thereby. The mast-head is mounted to the top of the mast assembly, facilitating joinder of the horizontal boom section to the mast. The mast-head includes a rotation drive for rotating the boom structure. A counterweight structure may also be mounted to the mast-head, opposing the torque created by the weight of the boom structure.
The mast is preferably rigid, resistant to torque, and transmits out-of-vertical forces to the chassis without adversely affecting operation of the elevation system. In a preferred embodiment, a composite mast, formed of a two-by-two square grouping of hollow square-section tubes provides such rigidity and strength. The mast assembly further preferably includes a guide for the mast, which includes four similar hollow square-section tubes fixed to the chassis outwardly of the corners of the mast, and rollers between the mast corners and the inner corners of the guide. Preferably, several sets of rollers are positioned at varying heights along the mast. The rollers permit translation of the mast relative to the guide, which is fixed to the chassis, but transmit to that chassis the forces out of the vertical, created by torque of the weight of a boom or load. The elevation system also preferably includes a screw and a screw jack, which require little power for operation and are very reliable. This system has advantages over alternatives, such as a hydraulic lift for a similar mast, or a mast formed of a hydraulic piston. The weight and cost of an additional latching system are avoided by using the screw jack system, which does not depend upon a hydraulic power source for lift, and can maintain position without power input. The present invention also avoids compression and failure of hydraulic seals by omitting them and transmitting any lateral loads via rollers, which are designed to transmit this load to the guide.
In a further preferred embodiment, loads supported by the boom sections include their own weight and sensors for detecting transmitted radiation for inspecting vehicles and containers inward of and below the boom. Various types of sensors may be used, such as transmission, backscatter, sidescatter and forward scatter detectors. In this preferred embodiment, the boom structure is mounted on a mast, itself mounted to the chassis of a mobile transport. The boom sections may be rotated relative to the mast, to a position in which they extend roughly perpendicular to the transport""s direction of forward travel. The bottom end of the vertical boom section preferably extends proximate the ground surface. In this position, the horizontal and vertical boom sections form, with the adjacent side of the transport, an essentially planar rectangular scanning zone. A radiation source, typically an X-ray emitter, is mounted on the mobile transport, along with the necessary support equipment, power source and operator. The X-ray device emits penetrating radiation into the scanning zone and toward sensors mounted upon the inward face of the vertical boom section, and upon the lower face of the horizontal boom section. The X-ray device may provide coverage of the scanning zone by repeatedly sweeping a narrowly focussed beam aligned to the plane, or by other techniques permitting radiation transmission covering a planar area. If the radiation would tend to penetrate the sensor, or the boom""s structural material, additional absorptive material, such as lead, may be employed to do so.
The further scope of the invention will become apparent upon the review of the detailed description of the preferred embodiments. It should however be understood that these descriptions do not limit the scope of the invention and are given as examples only, and that various changes and modifications which are fully within the scope of the present invention will become apparent to those skilled in the art.